Sound reproducer



' Jly 28, 1959 1 A. BURKE 2,897,291

souNn REPRoDucER f Filed Dec. 12, 1955 Anja SOUND REPRODUCER `Ambrose Burke, Scituate, RJ.

Application December 12, 1955, Serial No. '552,315

3 Claims. (Cl. 179-115.5)

This invention pertains `generally to sound reproducers, and more specifically, to a loudspeaker of the electrodynamic or moving-coil type.

A primary object of the instant invention is the provision of a loudspeaker which will supply more harmonics or overtones than heretofore, thereby providing sound which, in effect, appears to be more three dimensional in scope and less flat than sound reproduced by conventional speakers heretofore utilized.

Another object of the instant invention is the provision of a loudspeaker capable of utilizing a greater output from a transformer while at the same time producing sharp and distinct tones.

Still another object is the provision of a speaker which has virtually no resonant frequency such as usually caused by cone vibration, and which smooths out and reduces the gain or such caused by an audio frequency.

A further object is the provision of a speaker which is exceedingly effective at low frequencies.

Another object of the instant invention is the provision of a loudspeaker which, although simple of construction, is nevertheless highly efficient and sensitive in operation.

Other objects, features and advantages of the invention will become apparent as the description thereof` proceeds when considered in connection With the accompanying illustrative drawings.

In the drawings which illustrate the best mode presently contemplated by me for carrying out my invention:

Fig. 1 is a front elevation of a loudspeaker embodying the instant invention;

Fig. 2 is a rear elevation thereof, partly broken away;

Fig. 3 is an enlarged section taken on line 3--3 of Fig. 2; and

Fig. 4 is detail section, partly broken away, of the outer armature utilized in the instant invention.

The conventional electrodynamic loudspeaker or sound reproducer as heretofore utilized, has worked onthe principle of a moving voice coil, which, when excited, usually by magnetic means, imparts vibration to the speaker cone thereby producing sound. More specifically, the moving voice coil is usually wound on a cardboard bobbin or the like which in turn is secured to the speaker cone. A magnetic field is provided proximate to said voice coil and the electrodynamic action which results between the flux produced by current passing through the Wires of said coil and the magnetic lines of force creates a mechanical upward and downward pulling action. This force causes the voice coil to move up and down, which in turn makes the speaker cone vibrate and produce sound. The volume from the speaker is determined by the strength of the magnetic field, the number of turns in the voice coil, and the amount of current passing therethrough.

It has been found that the above-described speaker operation can be greatly improved by the use of double voice coils, concentrically disposed. By setting up the two coils so that they each coact with separate and independent magnetic elds and function in unison, the sound output is States Patent@ 2,897,291 Patented July 28, 1959 fice aluminum cylinder 24 having windings 26 therearound.

A cork or composition ring 28 is secured to the inner surface of the cylinder 24 and acts as both spacing and insulating means between outer coil bobbin 22 and an inner Voice coil 30, likewise comprising a cardboard or aluminum cylinder having windings therearound. i It will be understood that the voice coil bobbin 30 is secured to the spacer 2,8 and is maintained solely thereby in concentric relation with respect tov outer voice coil bobbin 2.2. It will further be understood that the bobbins 22 and 30, other than the formers connection to speaker cone 18, are not anchored in any way and hence are free to move axially whereby to impart vibration tothe speaker cone 18.

Secured to the truncated end of shell 12 by any de-v sirable means, `as at 32, is a metallic rectangular supporting strap 34. Supporting strap 34 comprises a rear wall 36, side walls 38 and a front wall 40 having therein a centrally disposed aperture 42, the inner surface 43 of which comprises a pole face. Mounted on the inner surface of rear wall as by cementing or the like is a permanent magnet 44, although it will be understoodl that other forms and types of magnets, such as an electromagnet, for example, could well be utilized. Magnet'44 at its free forward surface engages inner and outer poles 46 and 48, respectively, now to be described. It will be understood that poles 46 and 48 are each constructed of magnetic steel and hence, due to their contact with magnet 44, provide their respective magnetic fields. The outer pole 48 comprises a tubular body portion 50, the outer diameter of which extends through the aperture 42 in spaced relation to pole face 43 thereof whereby to p-rovide a gap 51. Pole 48 further comprises an outwardly extending peripheral flange 52 which is in contact with magnet 44. Inner pole 46 comprises a core portion 54, and likewise is provided with an outwardly extending ange 56. As will be noted, inner pole 46 is mounted concentrically Within outer pole 48 by virtue of the fact that ange 56 is a press-tit therein. A circular spacer ring 57 of non-magnetic material, such as brass, maintains outer pole 48 against longitudinal movement, and

also maintains poles 46 and 48 centered with respect to the aperture 42.

In operation and use, outer voice coil bobbin 2.2 surrounds outer pole 48 in very close proximity thereto and extends into gap 51, while inner voice coil bobbin 30is disposed intermediate core 54 of the inner pole and tubular portion 50 of the outer pole. As will be noted clearly in Fig. 3, tubular portion 50 does not extend inwardly of gap 51, thereby leaving uncovered a substantial portion Vof the windings on bobbin 30. As will hereinafter beof being magnetized or attracted by a magnet, some examples of such material being so-called white metal, brass, aluminum, copper, etc.

Another important feature of the instant invention resides in the fact that the space 59' between voice coil bobbins 22 and 30 acts, in effect, as a sound-compression chamber. ln other words, the sound vibration waves which emanate from the outer bobbin 22 will be carried across the chamber 59 and imparted to the inner bobbin 30 and vice versa. Hence, in eiect, each voice coil bobbin cooperates with the other to produce more pronounced vibration of the speaker cone. In this respect, i-t might be pointed out that the windings on either bobbin 22 or 30 could be eliminated, and the loudspeaker would still function in improved fashion. More specifically, if, for example, ythe windings 26 of outer bobbin 22 were eliminated, the vibrations emanating from inner bobbin 30 would still move across chamber 59 and be imparted to the cylinder 24, thereby causing the latter to aid in vibrating the speaker cone.

Conventional terminals 60 and 62 and wiring 64 and 66 are provided for the energization of the voice coils. Also, a conventional spider 68 may be utilized, if desired, to help maintain the voice coils in proper position and also to act as a dust shield. In fact, it will be understood that the entire construction of the speaker assembly set forth and described herein is of a conventional nature with the exception of the double voice coils and the inner and outer poles described above.

While there is shown and described herein certain specic structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be -m-ade without def parting from the spirit and scope of the underlying inventive concept. For example, it would be a simple matter to re-design the poles so that they would be movable with the speaker cone 18, while the voice coil bobbins, in turn, would be iixedly mounted. Therefore, the instant invention is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

I claim:

1. A loudspeaker of the electrodynamic type, comprising a substantially frustro-conical speaker cone, rst and second voice coil bobbins mounted concentrically with respect to'each other, means securing one of said voice coil bobbins to said speaker cone in yaxially extending relation therefrom, means comprising an insulating and spacing collar attached to one of said voice coil bobbins and attached to and supporting said other voice coil bobbin in spaced relation and dening therebetween an annular sound compression chamber, means for creating a magnetic eld in juxtaposition to each of said bobbins, said magnetic means comprising a first pole having ya core portion extending within the inner of said bobbins, a second pole comprising a tubular portion extending into said sound compression chamber, and pole faces disposed adjacent the outer surface ofthe outer of said bobbins and cooperating with said second pole to form a gap, said second pole tubular portion having on the inner surface a non-magnetic metallic coating to isolate the magnetic eld of said second pole from the magnetic ield of said rst pole.

2. A loudspeaker of the electrodynamic type, comprising a substantially frustro-conical speaker cone, inner and outer voice coil bobbins mounted concentrically with respect to each other, means securing said outer voice coil bobbin to said speaker cone in axially extending relation therefrom, a spacing collar of magnetic insulating material secured to both said inner and outer voice coil bobbins -to rigidly support said bobbins in concentric relationship and to define an annular sound compression chamber therebetween, means for creating a magnetic field in juxtaposition to each of said bobbins, said magnetic means comprising a permanent magnetic, a trst pole attached to said permanent magnetic and provided with a core portion extending within 4the inner voice coil bobbin, a second pole attached to said permanent magnetic and mounted concentrically with respect to said trst pole and provided with a tubular portion extending into said sound compression chamber, a gap formed between said rst and second poles, said second pole tubular portion having on the inner surface a non-magnetic metallic coating to control the eective force of the magnetic eld of said tirst pole.

3. A loudspeaker of the electrodynamic type, comprising a substantially frustro-conical speaker cone, inner and outer voice coil bobbins mounted concentrically with respect to each other, means securing said outer voice coil bobbin to said speaker cone in axially extending relation therefrom, a spacing collar of magnetic insulating material secured to both said inner and outer voice coil bobbins to rigidly support said bobbins in concentric relationship and to dene an annular sound compression chamber therebetween, means for creating a magnetic field consisting of a circular strap having an axial orifice and open opposite sides, a block formed in the circular strap opposite the axial orilce, said circular strap and block comprising a low loss permanent magnetic circuit, a iirst pole bar magnet attached to said block and provided with a core portion extending within the inner voice coil bobbin, a second pole attached to said block, mounted concentrically with respect to said irst pole and provided with a tubular portion extending into said sound compression chamber and forming part of said low loss magnetic circuit, the forward surface of said second pole forming the other end of said sound compression chamber, said inner and outer voice coil bobbins and said rst and second poles extending axially through said axial orifice to form a irst gap between said circular strap at said axial orifice and said outer voice coil bobbin, and a second gap formed between said rst and second poles, said second pole tubular portion having on the inner surface a non-magnetic metallic coating to control the eilective magnetic field between said rst pole bar magnetic and said second pole low loss magnetic circuit.

References Cited in the le of this patent UNITED STATES PATENTS l,842,770 Thompson Jan. 26, 1932 2,007,746 Ringel July 9, 1935 2,269,284 Olson lan. 6, 1942 2,539,672 Olson et al. Jan. 30, 1951 2,699,472 Olson et al. Jan. 1l, 1955 v Y FOREIGN PATENTS 715,389 France Dec. 2, 1931 

